The mechanical deformability properties of blood cells are not only essential determinants of flow distribution in the microcirculation but also modulate cell aggregation, agglutination, and other types of adhesive interactions. The initial stage of cell-surface "recognition" is quantitated by the chemical affinity between opposite surfaces; this is an important factor in removal of aberrant cells and material from the circulation, bacterial and viral infection of cells, and arrest and margination of circulating white cells and tumor cells. Viability of cell-cell contacts when exposed to disruption by shear forces in the circulation is related to the strength of adhesion which, in turn, depends on the extent of contact and the mechanics of separation. Hence, the objectives of this application are to quantitate the time-dependent mechanical properties of blood cells, the energetics of blood cell deformation and chemical attraction in cell-cell adhesion, and the mechanics of separation of adhesive contacts. The specific aims are to: (1) Relate the mechanical properties of blood granulocytes to the structural components of the cell; compare active and passive deformation properties of granulocytes; investigate membrane continuity and the degranulation process during cell activity; measure the motive force in phagocytosis and the effect of disruptors of cell structural components. (2) Measure the mechanical stiffening of red cell membranes caused by binding of adhesive ligands (e.g. "adhesins" shed from bacteria; agglutinating antibodies); measure the potential for formation of adhesive contact in these ligands; measure and model the detailed mechanics of separation of adhesive contacts; measure adhesivity of blood cells to cultured vascular endothelium. (3) Measure the kinetics and binding of fluorescently labelled ligands to single red cells; determine the relation between strength of adhesion, time course and magnitude of ligand binding; evaluate augmentation of adhesive strength by accumulation of material into cell-cell contact zones as cells are separated. Blood cell deformability and adhesion experiments utilize unique multi-micromanipulation techniques; the observations are recorded with a video-microscope system. Surface binding and kinetics of ligand-receptor complexes are measured with a laser microfluorometry system.